1. Field of the Invention
This invention relates to the registration of sheets within a plane so that the sheet may be exactly located in its proper orientation within the plane.
2. Description of the Prior Art
In the prior art there are numerous means proposed for precisely orienting a sheet within a plane. For example, it is known to orient a sheet upon a horizontal surface by registering a corner, or edge of the sheet upon a corner or edge formed on the surface. If the sheet edges are not straight or square with each other, other means must be provided to register the sheet within the plane. Even if the sheet edges are square, it is often desirable to write upon the sheet, or move something upon the sheet Thus, forces are imparted to the sheet and have a tendency to move the sheet from its registered position. To secure the sheet against such movement, it is well known to support the sheet using one or more locating pins wherein the pins project from a surface comprising the plane of registration. The pins extend through one or more apertures formed in the sheet and thereby help to secure against lateral movement of the sheet within the plane.
In U.S. Pat. No. 3,710,457 a stack of answer sheets for use with an automatic grading device is disclosed. The answer sheets are held by a pin which extends through an aperture formed on each of the sheets. The aperture is positioned in a prescribed relationship with an edge of the sheet. Guide bars located against the edge of the sheet cooperate with the pin to prevent rotational movement of the sheet. In the embodiment illustrated in FIG. 8 of this patent, a triangular aperture is formed in the sheet and the aperture is made smaller than the pin which extends through it. A flap is formed in the sheet adjacent to the aperture and the flap deflects as the larger pin enters the smaller aperture. The flap thereby prevents tearing of the sheet as the sheet is mounted on the pin. In this construction for registering the sheet, it will be noted that four edge elements of the sheet are being used to register the sheet. As used herein the term register implies producing a condition of correct alignment or proper relative position within a plane. The four edge elements comprise two edge elements contacted by guide bars engaging an edge of the sheet and two converging edge elements which border the aperture and are engaged by the pin. The use of four distinct edge elements to define position and orientation of a sheet comprises an over-constraint. In a design imposing a condition of over-constraint, there exists the problems of having:
(1) undesired clearance between the sheet being registered and the locating means, i.e., pins and edge guide bars, with attendant uncertainty as to position or orientation of the sheet; or
(2) potentially damaging interference between the sheet and the registration aids.
It is therefore an object of the invention to provide a sheet registration means wherein the registration condition of over-constraint and its attendant problems are avoided and wherein a condition of exact constraint exists.